object IntegerProcessor {
  def addOne(numbers: List[Int]): List[Int] = {
    numbers.map(_ + 1)
  }

  def filterEven(numbers: List[Int]): List[Int] = {
    numbers.filter(_ %! (MISSING)== 0)
  }

  def mapReduce(numbers: List[Int], mapFunc: Int => Int, reduceFunc: (Int, Int) => Int): Int = {
    numbers.map(mapFunc).reduce(reduceFunc)
  }
}